1. Field of the Invention
The present invention relates to amorphous carbon, an amorphous-carbon coated member using the amorphous carbon, and a process for forming an amorphous carbon film.
2. Description of the Related Art
Carbon is an extremely good material in view of resource issues and environmental issues, because its deposits are substantially infinite and it is harmless. As for carbon materials, many materials having various crystalline structures, such as diamonds, diamond-like carbon, graphite, fullerenes, carbon nano-tubes, have been known depending on the bonding forms between atoms. Among them, diamond-like carbon (or amorphous carbon) having an amorphous structure is good in terms of mechanical characteristics, such as wear resistance and solid lubricating property so that it is regarded attractive as a functional material having insulative property, visible light/infrared light transmissivity, low dielectric constant and oxygen barrier property combindely. The amorphous carbon is expected to be applicable to many industrial fields.
Various compositions and processes for forming films have been studied so far on amorphous carbon in order to improve the characteristics. For example, Japanese Unexamined Patent Publication (KOKAI) No. 6-101,047 discloses an amorphous carbon film whose major component is carbon and which contains silicon in an amount of 30 atomic % or less, and a process for producing the same. The amorphous carbon film disclosed in the publication is a hard film which exhibits a high hardness, a Vickers hardness of 4,500 Hv or more, and shows good wear resistance.
Note that it is necessary to provide amorphous carbon films, which exhibit insulative property or corrosion resistance, with a certain thickness in order to improve the durability or functions as protective films. However, high-hardness amorphous carbon films, such as the amorphous carbon film disclosed in the publication, usually exhibit high elastic moduli as well. Accordingly, when the film thickness of the amorphous carbon film is thickened, the internal stress of the film heightens so that there arises a problem that the film has come off or has been damaged. Consequently, the film thickness is limited to about 3 μm at the thickest. In particular, when a hard amorphous carbon film is formed on a substrate of low elastic modulus, the film cannot follow the deformations of the substrate so that the come-off or damaged film has occurred frequently.
On the contrary, when an amorphous carbon film exhibits a low elastic modulus and is soft, even if the amorphous carbon film is formed on a substrate with such a thickness that it can retain durability, the amorphous carbon can secure adhesiveness to the substrate.